Valley watercourses (Maltese: widien) are one of the most species-rich habitats on a national scale. However, they are considered as one of the most endangered habitats in the Maltese Islands.

The species community associated with a watercourse is by nature dynamic, and its integrity depends on the amount and frequency of rainfall, as well as other abiotic factors, for instance the rate of siltation.

In general, the greater part of local plant and animal species reliant of water during some part of their life-cycle are found in valley watercourses.

Various annual and perennial plants colonise the watercourse, some of which are rare on a national scale, in view of the restricted distribution of their habitat.

One can mention the very rare perennial willow-leaved knotgrass (scientific: persicaria salicifolia; Maltese: persikarja tal-baħrija). Various herbaceaous perennials grow in watercourses, noting that perennial plants are able to withstand periods of dryness.

Watercourse plants require a good underground system of roots or rhizomes for anchorage, noting the unstable watercourse substrate. One of the most common plants to colonise valleys is the giant reed (scientific: arundo donax; Maltese: qasba kbira). Encroachment by this reed results in reduction of water current; however, when the water passes through the rhizomes of this plant, the water is filtered from nutrients. The giant reed is often replaced by the common reed (scientific: phragmites australis; Maltese: qasbet ir-riħ) at the mouth of valley watercourses where freshwater feeds into the sea.

Should you require more information, please contact nature.

requests@mepa.org.mt.